Wednesday, November 14, 2007

The Most Accurate Measurement Ever Made

Would you ever think that using single photons and an interferometer, one could get the most accurate measurement ever made up to now? One certainly can, as shown by this very elegant experiment (link may be available for free for a limited time). In fact, they got close to the Heisenberg Uncertainty limit!

But Pryde and his coworkers in Australia have demonstrated a way of reaching the Heisenberg limit of measurement precision without needing these elusive states: by looking at photons traversing an interferometer's arms one at a time. The key is to avoid making measurements that determine which arm the photon is in, until the beams are recombined at the end. This allows the shot noise to be more or less smoothed away.